The invention relates to a process for the cultivation of biological cells in a non-solid cultivation environment, especially a process for the cultivation of cells, in which biological cells are arranged on at least one boundary surface between liquid and/or gaseous cultivation phases, and to a cultivation apparatus for carrying out such a process.
The cultivation (growth, multiplication and/or differentiation) of biological cells takes place in the practice typically on solid surfaces such as, e.g., on the bottom of a Petri dish or on other cultivation substrates. During the growth in an in vitro cell culture cell monolayers or layered tissue formations form on the solid surface whose form corresponds to the shape of the surface. The cultivation on solid surfaces has the disadvantage that the cells in the cellular union develop under geometric conditions that are determined by the shape of the surface of the cultivation substrate and as a rule do not correspond to the natural conditions. The formation of natural structures in the cellular union is hindered by the cellular culture being shaped by the shape of the surface. A further disadvantage of the in vitro cultivation on a solid surface results from the molecular adhesion of the cells to the surface. Adherent bonds are formed between the cells and the surface by adhesive proteins, e.g., of the integrin family, that must be loosened during manipulations of the cellular culture. For example, a transfer of cells onto another substrate requires an enzymatic treatment, e.g., with trypsin or a mechanical scratching off of the cells from the surface. In both instances a significant stress for the cells and a cellular loss cannot be avoided.
In order to avoid the shaping of the cellular culture by the surface shape of a solid substrate, DE 10 2004 025 086.3 describes the use of a host egg as incubator for in vitro cultures. This advantageously creates cultivation conditions that come the closest to the natural growth conditions as regards the geometric conditions and the supply of nutrients. However, this technique has the disadvantage that the environmental conditions during the cultivation of cells are given by the properties of the host egg used.
The cultivation of individual cells or cellular groups in suspended drops of a liquid cultivation medium as is schematically shown in FIG. 31 is known from the practice of the cultivation of stem cells. Conditions are advantageously given in the suspended drop that are similar to the geometric conditions of the growth, e.g., in an egg. The cells can freely move in the liquid cultivation medium on the curved inner surface of the suspended drop and form cell groups or cell unions. However, a decisive disadvantage of this technique resides in the limited size of the suspended drops. The drops can only have diameters up to a few millimeters so that the cultivation time and the size of the cultivated cell groups are correspondingly limited.
The holding of cell cultures in bioreactors (diffusion reactors, fermenters) is known in order to obtain substances that are produced by the cells (see, for example, G. M. Zijlstra et al. in “Current opinion in biotechnology”, volume 9, 1998, pp. 171-176; C. T. MacLeod et al. in “Process Biochemistry”, volume 40, 2005, pp. 1799-1805; A. J. Daugulis in “Current opinion in biotechnology”, volume 8, 1997, pp. 169-174; M. G. Antov et al. in “Enzyme Microbial. Technol.”, volume 28, 2001, pp. 467-472; and K. G. Clarke et al. in “Biochem. Eng. J.” volume 28, 2006, pp. 237-242). Typically, a liquid multiphase system of several immiscible phases is contained in a bioreactor and substances produced by the cells in a first phase diffuse into an adjacent phase and are removed from there. Accordingly, a retroaction of the substances on the cells in the first phase is avoided. The use of the conventional bioreactors is limited to biotechnological functions such as, for example, the production of substances. Cultivation conditions can be adjusted with a bioreactor under which the cells are viable and produce the desired substance. However, the conventional bioreactors are not suitable for cultivation tasks of the cellular biology such as, for example, the above-cited cultivation of cells in the cellular union.
The invention has the objective of providing an improved process for the cultivation of biological cells with which the disadvantages of the conventional cultivation techniques are overcome. The process should make a cell cultivation possible, in particular under conditions that are not influenced by the shape or size of a cultivation container and at the same time make possible an adaptation to natural conditions of the growth, the multiplication and/or the differentiation of cells. Furthermore, the objective of the invention is to provide a cultivation apparatus with which the disadvantages of the conventional cultivation apparatuses for the in vitro cultivation of biological cells are overcome.
These objectives are solved by a cell cultivation process or a cultivation apparatus of the invention.